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block, cfq: move ioc ioprio/cgroup changed handling to cic
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ioprio/cgroup change was handled by marking the changed state in ioc
and, on the following access to the ioc, performing RCU-protected
iteration through all cic's grabbing the matching queue_lock.

This patch moves the changed state to each cic.  When ioprio or cgroup
changes, the respective bit is set on all cic's of the ioc and when
each of those cic (not ioc) is accessed, change is applied for that
specific ioc-queue pair.

This also fixes the following two race conditions between setting and
clearing of changed states.

* Missing barrier between assign/load of ioprio and ioprio_changed
  allowed applying old ioprio.

* Change requests could happen between application of change and
  clearing of changed variables.

Signed-off-by: Tejun Heo <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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htejun authored and axboe committed Dec 13, 2011
1 parent 283287a commit dc86900
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Showing 5 changed files with 65 additions and 27 deletions.
2 changes: 1 addition & 1 deletion block/blk-cgroup.c
Original file line number Diff line number Diff line change
Expand Up @@ -1648,7 +1648,7 @@ static void blkiocg_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
/* we don't lose anything even if ioc allocation fails */
ioc = get_task_io_context(tsk, GFP_ATOMIC, NUMA_NO_NODE);
if (ioc) {
ioc->cgroup_changed = 1;
ioc_cgroup_changed(ioc);
put_io_context(ioc);
}
}
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45 changes: 45 additions & 0 deletions block/blk-ioc.c
Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,51 @@ struct io_context *get_task_io_context(struct task_struct *task,
}
EXPORT_SYMBOL(get_task_io_context);

void ioc_set_changed(struct io_context *ioc, int which)
{
struct cfq_io_context *cic;
struct hlist_node *n;

hlist_for_each_entry(cic, n, &ioc->cic_list, cic_list)
set_bit(which, &cic->changed);
}

/**
* ioc_ioprio_changed - notify ioprio change
* @ioc: io_context of interest
* @ioprio: new ioprio
*
* @ioc's ioprio has changed to @ioprio. Set %CIC_IOPRIO_CHANGED for all
* cic's. iosched is responsible for checking the bit and applying it on
* request issue path.
*/
void ioc_ioprio_changed(struct io_context *ioc, int ioprio)
{
unsigned long flags;

spin_lock_irqsave(&ioc->lock, flags);
ioc->ioprio = ioprio;
ioc_set_changed(ioc, CIC_IOPRIO_CHANGED);
spin_unlock_irqrestore(&ioc->lock, flags);
}

/**
* ioc_cgroup_changed - notify cgroup change
* @ioc: io_context of interest
*
* @ioc's cgroup has changed. Set %CIC_CGROUP_CHANGED for all cic's.
* iosched is responsible for checking the bit and applying it on request
* issue path.
*/
void ioc_cgroup_changed(struct io_context *ioc)
{
unsigned long flags;

spin_lock_irqsave(&ioc->lock, flags);
ioc_set_changed(ioc, CIC_CGROUP_CHANGED);
spin_unlock_irqrestore(&ioc->lock, flags);
}

static int __init blk_ioc_init(void)
{
iocontext_cachep = kmem_cache_create("blkdev_ioc",
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28 changes: 9 additions & 19 deletions block/cfq-iosched.c
Original file line number Diff line number Diff line change
Expand Up @@ -2904,7 +2904,7 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
cfq_clear_cfqq_prio_changed(cfqq);
}

static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
static void changed_ioprio(struct cfq_io_context *cic)
{
struct cfq_data *cfqd = cic_to_cfqd(cic);
struct cfq_queue *cfqq;
Expand Down Expand Up @@ -2933,12 +2933,6 @@ static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_ioc_set_ioprio(struct io_context *ioc)
{
call_for_each_cic(ioc, changed_ioprio);
ioc->ioprio_changed = 0;
}

static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
pid_t pid, bool is_sync)
{
Expand All @@ -2960,7 +2954,7 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
}

#ifdef CONFIG_CFQ_GROUP_IOSCHED
static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic)
static void changed_cgroup(struct cfq_io_context *cic)
{
struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);
struct cfq_data *cfqd = cic_to_cfqd(cic);
Expand All @@ -2986,12 +2980,6 @@ static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic)

spin_unlock_irqrestore(q->queue_lock, flags);
}

static void cfq_ioc_set_cgroup(struct io_context *ioc)
{
call_for_each_cic(ioc, changed_cgroup);
ioc->cgroup_changed = 0;
}
#endif /* CONFIG_CFQ_GROUP_IOSCHED */

static struct cfq_queue *
Expand Down Expand Up @@ -3222,13 +3210,15 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
out:
get_io_context(ioc);

if (unlikely(ioc->ioprio_changed))
cfq_ioc_set_ioprio(ioc);

if (unlikely(cic->changed)) {
if (test_and_clear_bit(CIC_IOPRIO_CHANGED, &cic->changed))
changed_ioprio(cic);
#ifdef CONFIG_CFQ_GROUP_IOSCHED
if (unlikely(ioc->cgroup_changed))
cfq_ioc_set_cgroup(ioc);
if (test_and_clear_bit(CIC_CGROUP_CHANGED, &cic->changed))
changed_cgroup(cic);
#endif
}

return cic;
err:
if (cic)
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3 changes: 1 addition & 2 deletions fs/ioprio.c
Original file line number Diff line number Diff line change
Expand Up @@ -50,8 +50,7 @@ int set_task_ioprio(struct task_struct *task, int ioprio)

ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
if (ioc) {
ioc->ioprio = ioprio;
ioc->ioprio_changed = 1;
ioc_ioprio_changed(ioc, ioprio);
put_io_context(ioc);
}

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14 changes: 9 additions & 5 deletions include/linux/iocontext.h
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,11 @@ struct cfq_ttime {
unsigned long ttime_mean;
};

enum {
CIC_IOPRIO_CHANGED,
CIC_CGROUP_CHANGED,
};

struct cfq_io_context {
void *key;
struct request_queue *q;
Expand All @@ -26,6 +31,8 @@ struct cfq_io_context {
struct list_head queue_list;
struct hlist_node cic_list;

unsigned long changed;

void (*dtor)(struct io_context *); /* destructor */
void (*exit)(struct io_context *); /* called on task exit */

Expand All @@ -44,11 +51,6 @@ struct io_context {
spinlock_t lock;

unsigned short ioprio;
unsigned short ioprio_changed;

#if defined(CONFIG_BLK_CGROUP) || defined(CONFIG_BLK_CGROUP_MODULE)
unsigned short cgroup_changed;
#endif

/*
* For request batching
Expand Down Expand Up @@ -81,6 +83,8 @@ void put_io_context(struct io_context *ioc);
void exit_io_context(struct task_struct *task);
struct io_context *get_task_io_context(struct task_struct *task,
gfp_t gfp_flags, int node);
void ioc_ioprio_changed(struct io_context *ioc, int ioprio);
void ioc_cgroup_changed(struct io_context *ioc);
#else
struct io_context;
static inline void put_io_context(struct io_context *ioc) { }
Expand Down

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